1. Field of the Invention
The present invention relates to a scroll-type fluid displacement apparatus, and more particularly, to a spiral starting portion of a fixed scroll and an orbiting scroll.
2. Description of Related Art
Scroll-type fluid displacement apparatus are known in the art. For example, U.S. Pat. No. 5,037,279, which is incorporated herein by reference, describes spiral portions of a fixed scroll and an orbiting scroll.
Referring to FIGS. 5 to 7a-d, an orbiting scroll 50 has an end plate 50a; an involute spiral wrap element 50b, which extends from a first side of end plate 50a; and an annular boss 50c, which extends from a second side of end plate 50a. An involute spiral wrap element 40b of a fixed scroll (not shown) is formed on an end plate of the fixed scroll and is symmetrical to spiral element 50b of orbiting scroll 50. Orbiting scroll 50 is supported on a housing by an Oldham coupling mechanism consisting of an Oldham coupling ring and Oldham coupling keys. The Oldham coupling mechanism prevents the rotation of orbiting scroll 50 on its axis and generates an orbital motion with respect to the fixed scroll.
As shown in FIGS. 5 and 6, a widened-starting portion 500c of spiral element 50b of orbiting scroll 50 has a cross-sectional shape, in which the thickness is greater at the base surface and less at the tip surface (i.e., the thickness decreases or tapers from the base surface to the tip surface). An exterior curve 506, which is a radially exterior curve between a first tip point 501 at the tip and a first widened-starting point 503 at the base surface, is an involute curve. An interior curve 507, which is a radially interior curve between a second tip point 502 at the tip surface and a second widened-starting point 505 at the base surface, also is an involute curve. A spiral base portion between point 503 and point 505 is composed of the curved line, described below. A region between point 503 and a point 504 is defined by a first convex arc 509. A radius r of the convex arc 509 is defined by the following equation:   r  =                    4        ⁢                              a            2                    ⁡                      (                                          λ                1                2                            +              1                        )                              -              ϵ        2                    4      ⁢              (                  ϵ          +                      2            ⁢            a            ⁢                          xe2x80x83                        ⁢                          λ              1                                      )            
where:
a is a radius of an involute base circle;
xcex1 is a widened-starting angle; and
xcex5 is an orbit radius.
A region between point 504 and point 505 is defined by a second concave arc 510. A radius R of the concave arc 510 is defined by the following equation:
R=r+xcex5
On the other hand, the region between point 501 and point 502 at the tip of spiral element 50b is defined by an arc 508, the diameter of which substantially corresponds to a distance between opposed walls of the involute curve of spiral element 50b. A curve along the base from point 503 to point 505 and a curve along the tip from point 501 to point 502 are connected through a smooth inclined wall.
Referring to the compression and discharge strokes of the known scroll-type compressor, FIG. 7a shows the known compressor in a condition, in which the suction stroke has been completed and the compression stroke has just begun. Thereafter, the strokes proceed in sequence, as shown FIGS. 7b, 7c and 7d, and a compression chamber 60 gradually moves towards the center like a compression chamber 60xe2x80x2, as shown in FIG. 7a, while its volume decreases. Consequently, compressed gas is discharged through a discharge port 61.
In the known scroll-type fluid displacement apparatus, however, as shown in a central portion of FIG. 7d, when compression is completed, fluid remains in a dead volume, which is defined by an inclined wall of spiral element 50b of orbiting scroll 50 and an inclined wall of spiral element 40b of the fixed scroll. The fluid in this dead volume expands, and interupts the drawing of new fluid into compression chamber 60. As a result, the compression efficiency of the scroll-type fluid displacement apparatus may be reduced.
Further, each of the tip points of spiral element 50b of orbiting scroll 50 and of spiral element 40b of the fixed scroll has a sharp edge shape. Therefore, when orbiting scroll 50 and the fixed scroll are operated in the compression and discharge strokes, defects may be created in the tip points of each spiral elements because both spiral element engage each other.
A technical advantage of the present invention is to reduce or eliminate the above-mentioned defects encountered in the spiral elements of the known scroll-type fluid displacement apparatus.
Another technical advantage of the present invention is to provide a scroll-type fluid displacement apparatus, which has increased strength in the central portions of spiral elements of an orbiting scroll and a fixed scroll.
A further technical advantage of the present invention is to provide the scroll-type fluid displacement apparatus, which has increased volmetric efficiency, e.g., compression efficiency, expansion efficiency, and discharge efficiency.
In an embodiment of this invention, a scroll-type fluid displacement apparatus comprises a rear housing and a front housing, a fixed scroll and an orbiting scroll, a driving mechanism, and a rotation preventing mechanism. The rear housing has an open end and an inlet port and an outlet port. A front housing closes the open end of the rear housing. The fixed scroll has a first end plate and a spiral element formed on and extending from a first side of the first end plate. The fixed scroll is attached to the rear housing. The orbiting scroll has a second end plate and a spiral element formed on and extending from a first side of the second end plate. Each of the spiral elements interfits with the other at an angular and a radial offset to form a plurality of line contacts defining at least one pair of sealed-off fluid pockets. A driving mechanism includes a drive shaft rotatably supported by the front housing to effect the orbital motion of the orbiting scroll by rotation of the drive shaft to thereby change the volume of the fluid pockets. A rotation preventing mechanism prevents the orbiting scroll from rotating. An interior wall of a widened-starting portion of each of the spiral elements is inclined, such that the thickness of a base surface of the widened-starting portion is greater than the thickness at a tip surface and the thickness of the widened-starting portion gradually decreases towards the tip surface of the widened-starting portion. A first transition line between the interior wall and the tip surface comprises a first upper arc ending at an upper, interior involute wall starting point and a second upper arc beginning at an upper, exterior involute wall starting point. A second transition line between the interior wall and the base surface comprises a first lower arc ending at the lower, interior involute wall starting point and a second lower small arc beginning at the lower, exterior involute wall starting point.
Other objects, features, and advantages will be apparent to persons of ordinary skill in the art from the following detailed description of the invention and the accompanying drawings.